A semiconductor device with a field effect transistor having a high breakdown voltage is used as an IC (Integrated Circuit) for controlling an LED (Light Emitting Diode) or an IC for controlling a power supply. As such a field effect transistor having a high breakdown voltage, an N channel-type field effect transistor with an N type well that is applied to a high voltage-side (high-side) will now be described.
An N type well is formed over a prescribed depth from a main surface of a semi conductor substrate (P type), and a P type well is formed in the N type well over a prescribed depth from a surface thereof. An N type source region is formed in the P type well over a prescribed depth from a surface thereof. An N type drain region is formed to surround the P type well in a prescribed region of the N type well at a distance from the P type well, over a prescribed depth from a surface thereof. On a portion of the P type well and a portion of the N type well lying between the source region and the drain region, a gate electrode is formed with a gate insulating film interposed therebetween.
Moreover, a P type back gate contact region is formed in the P type well over a prescribed depth from a surface thereof, in order to keep the threshold voltage that is to be applied to the gate electrode for forming a channel, at a constant level. Within the P type well, N type source regions and P type back gate contact regions are arranged alternately in one direction (gate width direction).
In the N channel-type field effect transistor described above, when a voltage equal to or higher than the prescribed threshold voltage is applied to the gate electrode, a channel is formed in a portion of the P type well situated directly below the gate electrode, which causes a current to flow from the source toward the drain. Examples of documents disclosing field effect transistors having high breakdown voltages include Japanese Patent Laying-Open No. 05-267652 (Patent Document 1), Japanese Patent Laying-Open No. 2008-10628 (Patent Document 2), and Japanese Patent Laying-Open No. 11-307763 (Patent Document 3).